1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, which has a pattern formation process using a processed film or a resist.
2. Description of the Related Art
A resist pattern forming method in a lithography process will be described in brief. Assume in the following that a positive resist is used, where exposed portions are dissolved by a developer. Also, a plurality of semiconductor devices and semiconductor substrates during manufacturing are collectively called the “substrate.”
After a resist is coated on a processed film formed on a substrate, the resist is exposed. Then, the resist is developed to dissolve exposed portions of the resist in a developer, and the developer is washed away by pure water. Then, the substrate is dried to remove the pure water remaining on the substrate. A developing apparatus for performing the development process to a drying process will be described below.
FIG. 1 is a diagram for describing a developing apparatus. As illustrated in FIG. 1, the developing apparatus comprises stage 10 for holding substrate 200; stage driving unit 11 for rotating stage 10; cup 12 for recovering water coming off from substrate 200; a discharging mechanism for discharging developer onto substrate 200; and control unit 16 for controlling the respective components.
The discharging mechanism comprises hard pipe 17 for supplying a developer onto substrate 200; supporting rod 18 for supporting hard pipe 17; and a supporting rod driving unit 20 for advancing and retracting nozzle 14 of hard pipe 17 over and from substrate 200. Hard pipe 17 is connected to a developer tank (not shown) through flexible tube 19. Stage driving unit 11, discharge amount adjuster 15, and supporting rod driving unit 20 are connected to control unit 16 through communication lines, and operate in accordance with control signals from control unit 16. Control unit 16 has a program previously stored therein for causing the respective components to execute predetermined processes in a determined order.
The developing apparatus is also provided with a discharging mechanism for pure water in addition to the discharging mechanism for the developer. Since the discharging mechanism for pure water is similar in configuration to that for the developer, illustration thereof is omitted.
Next, a method of forming a resist pattern will be described in detail in connection with the operation of the developing apparatus illustrated in FIG. 1. FIGS. 2A to 2D are cross-sectional views illustrating a resist pattern forming method.
Semiconductor substrate 100 is prepared, with processed film 101 formed thereon. Resist 102 is coated on processed film 101 on this substrate by a spin-coat method, and baked (heated), followed by an exposure process which involves irradiating resist 102 with light at a predetermined wavelength through photo-mask 104, as illustrated in FIG. 2A.
Next, as the substrate is carried on stage 10 of the developing apparatus, control unit 16 operates supporting rod driving unit 20 for developer to move nozzle 14 above the substrate. Then, discharge amount adjuster 15 supplies a predetermined amount of developer to nozzle 14 in response to a control signal from control unit 16, causing the developer to be discharged onto the substrate from nozzle 14. As illustrated in FIG. 2B, developer 106 permeates over entire resist 102, as illustrated in FIG. 2B, and developer 106 dissolves exposed portions of resist 102.
After resist 102 has been soaked in the developer for a previously set time, control unit 16 operates supporting rod driving unit 20 for developer to move hard pipe 17 for developer to a position away from cup 12. Then, control unit 16 operates supporting rod driving unit 20 for pure water to move pure water nozzle 14 above the substrate. Then, control unit 16 transmits a supply control signal for supplying pure water to pure water discharge amount adjuster 15. Upon receipt of the supply control signal from control unit 16, pure water discharge amount adjuster 15 supplies a predetermined flow rate of pure water to nozzle 14. The pure water discharged from nozzle 14 washes away developer 106. In this event, control unit 16 may operate stage driving unit 11 to spin the substrate.
Next, as control unit 16 transmits a stop control signal to pure water discharge amount adjuster 15 to stop supplying the pure water, discharge amount adjuster 15, which receives the stop control signal, stops supplying the pure water. Even if the supply of the pure water stops, pure water 110 remains on the substrate, as illustrated in FIG. 2C, where pure water 110 permeates resist patterns 108.
Next, for conducting a spin dry which involves spinning the substrate about the center thereof to centrifugally shake off pure water 110, control unit 16 operates pure water supporting rod driving unit 20 to move pure water hard pipe 17 to a position away from cup 12, and then transmits a rotation control signal to stage driving unit 11 to rotate stage 10. Stage driving unit 11, which has received the rotation control signal, rotates stage 10 at a predetermined rotational speed. After shaking off the pure water on the substrate, as control unit 16 transmits a rotation stop signal to stage driving unit 11 for stopping the rotation of stage 10, stage driving unit 11, upon receipt of the rotation stop signal, stops the operation.
When pure water 110 is shaken off from the substrate by spin drying, as the level of pure water 110 lowers, patterns attract to each other due to surface tension caused by the water which permeates resist patterns 108, causing resist patterns 108 to incline, as illustrated in FIG. 2D. This phenomenon occurs with a higher probability when the aspect ratio (height/width), which is the ratio of the height to the width (length in the lateral direction in the figure) of illustrated resist patterns 108, is equal to or higher than three.
JP-A-2003-109897 discloses a method of solving the problem of resist patterns 108 which inclines due to spin drying. The method disclosed in this document replaces water with a low surface tension rinse liquid (organic solvent or the like). This method weakens the surface tension acting between resist patterns 108 during spin drying, thus preventing resist patterns 108 from inclining even if it has a high aspect ratio.
On the other hand, another method adds a rinse liquid including a surface-active agent to pure water before spin drying to reduce the surface tension of water.
However, the method using a low surface tension rinse liquid consumes a large amount of chemicals, thus causing a higher running costs and environmental problems because the liquid that is emitted as wasted fluid from the developing apparatus causes considerable damage to the environment. Also, this method has the problem that complete replacement is difficult because the method utilizes the difference in specific gravity between water and rinse liquid.
Also, for producing the effect of reducing surface tension by using a rinse liquid including a surface-active agent, the surface-active agent must be prepared so that it has a predetermined concentration or higher. As a larger amount of surface-active agent is included in pure water, a larger amount of surface-active agent also remains on the surface of the dried substrate. This can cause defects of water marks and the like, and the number of defects can amount to several thousands per substrate. Then, a similar problem can arise when pure water is removed from the substrate during the process of washing patterns made of a processed film. If several thousand defects occur per substrate, the yield rate will be significantly reduced.
While other methods can also be contemplated for solving the problem of inclining patterns, disadvantages of such methods will be described below. In a method for reducing the aspect ratio of a resist pattern, the film thickness of the resist is insufficient for etching in the next process, and can therefore fail to function as a mask. On the other hand, in a method for replacing water with a supercritical fluid of carbon dioxide (70 atmospheres) and for drying, not only expensive large-scaled apparatuses are required, but also deaeration, replacement, pressurization, and depression must be performed in order, resulting in long TAT (Turn Around Time). Further, a method for turning a substrate upside down for drying requires complicated and expensive apparatuses but is not effective for patterns that are inclined due to surface tension.